1. Field of the Invention
The invention relates to an optical sensor, which can be sterilized by irradiation, for determining at least one parameter in a medium, to a device with such an optical sensor, and to a method for producing the sensor and the device.
2. Description of the Related Art
Optical sensors are used, in particular, in disposable, mixing and bioreactors or containers in medical technology and biotechnology. In these and similar fields of application, it is often necessary to sterilize a container before use. In the field of disposable products, sterilization by radiation, more particularly gamma radiation, has proven its worth; however, this can be damaging to the optical sensors. Hence such sensors require an effective protective system that can simultaneously be implemented in a cost-effective fashion.
WO 02/056023 A1 and DE 10,051,220 A1 have disclosed optical sensors for measuring at least one parameter in a sample. These sensors are based on a device for exciting fluorescence in an analyte-sensitive fluorescent dye, which is immobilized in a sample vessel or reactor in a matrix and is in at least indirect contact with the sample, and an evaluation device for the resulting fluorescent response signal. The analyte concentration can be evaluated or determined here by using both the fluorescence decay time and the fluorescence intensity. A disadvantageous intrinsic problem of these sensor systems emerges from the photobleaching of the utilized fluorescent dyes, which is detrimental to the long-term performance of these sensors as a result of a gradual reduction in the signal-to-noise ratio. Photobleaching is caused both by the actual measurement and the associated excitation of the fluorophore by light with a suitable wavelength and by external light, which can for example pass through the wall of a transparent bioreactor from the outside. Furthermore, the measurement can be falsified by interaction between the fluorescence excitation light and the fluorophores present in the sample.
U.S. Pat. No. 7,390,462 B2 has disclosed a sensor in which the fluorescent dye is present in an immobilized fashion in a hydrophilic matrix. Said document claims a sensor with the pH-sensitive fluorescent dye MA-HPDS, present in a hydrogel. A disadvantage therein is that such hydrophilic optical sensors are damaged in a dose-dependent fashion during sterilization with gamma radiation. Such radiation is particularly applied in laboratory technology in the case of containers made of polymers. Both the intensity of the fluorescence of the dye or dyes and the sensitivity of the sensor with respect to the measurement variable are reduced. Such a sensor is particularly damaged if, during the gamma sterilization, it is in contact with a relatively large volume of air or other conventional shielding gasses as well, such as nitrogen or argon. The gasses are partly ionized during the gamma sterilization. These ions and radical ions react with the walls during the sterilization of a gas-filled polymer container, but also with the dyes located in the sensors. Sensors based on porous, hydrophilic matrices are particularly susceptible to this because, as a result of the principles, the sensor chemicals have to present in immobilized fashion on the surface or inner surface of the matrix so that the sample to be measured can come into contact with the sensor chemicals. The extent of the damage firstly depends on the radiation dose and secondly depends on the surface-to-volume ratio of the irradiated container that contains the sensor. This ratio determines the number of ions and radical ions that damage the sensor or the sensor chemicals contained therein.
The invention is therefore based on the object of firstly developing an optical sensor and a device therewith, the sensitivity of which is reduced with respect to influences of external light, fluorophores, and radiation, more particularly gamma radiation, and secondly developing a method for the production thereof.